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Ulexite
pinacoidal | unit cell = a = 8.816(3) Å, b = 12.87Å, c = 6.678(1) Å; α = 90.25°, β = 109.12°, γ = 105.1°; Z = 2 | molweight = | color = Colorless to white | colour = | habit = Acicular to fibrous | system = Triclinic | twinning = Polysynthetic on {010} and {100} | cleavage = Perfect on {010} good on {1 0} poor on {110} | fracture = Uneven | tenacity = Brittle | mohs = 2.5 | luster = Vitreous; silky or satiny in fibrous aggregates | streak = White | diaphaneity = Transparent to opaque | gravity = 1.95 – 1.96 | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 1.491 – 1.496 nβ = 1.504 – 1.506 br/>nγ = 1.519 – 1.520 | birefringence = δ = 0.028 | pleochroism = | 2V = Measured: 73° to 78° | dispersion = | extinction = | length fast/slow = | fluorescence= May fluoresce yellow, greenish yellow, cream, white under SW and LW UV | absorption = | melt = | fusibility = | diagnostic = | solubility = Slightly soluble in water | other = Parallel fibrous masses can act as fiber optical light pipes | alteration = | references = Ulexite in Handbook of MineralogyUlexite at mindatUlexite at webmineral }} Ulexite (NaCaB5O6(OH)6•5(H2O)) (hydrated sodium calcium borate hydroxide), sometimes known as TV rock, is a mineral occurring in silky white rounded crystalline masses or in parallel fibers. The natural fibers of ulexite conduct light along their long axes, by internal reflection. Ulexite was named for the German chemist Georg Ludwig Ulex (1811–1883) who first discovered it. Ulexite is a structurally complex mineral, with a basic structure containing chains of sodium, water and hydroxide octahedra. The chains are linked together by calcium, water, hydroxide and oxygen polyhedra and massive boron units. The boron units have a formula of B5O6(OH)6 and a charge of −3. They are composed of three borate tetrahedra and two borate triangular groups. Ulexite is found in evaporite deposits and the precipitated ulexite commonly forms a "cotton ball" tuft of acicular crystals. Ulexite is frequently found associated with colemanite, borax, meyerhofferite, hydroboracite, probertite, glauberite, trona, mirabilite, calcite, gypsum and halite. It is found principally in California and Nevada, USA; Tarapacá Region in Chile, and Kazakhstan. Ulexite is also found in a vein-like bedding habit composed of closely-packed fibrous crystals. Ulexite is also known as TV rock due to its unusual optical characteristics. The fibers of ulexite act as optical fibers, transmitting light along their lengths by internal reflection. When a piece of ulexite is cut with flat polished faces perpendicular to the orientation of the fibers, a good-quality specimen will display an image of whatever surface is adjacent to its other side (as shown in the photograph). The fiber-optic effect is the result of the polarization of light into slow and fast rays within each fiber, the internal reflection of the slow ray and the refraction of the fast ray into the slow ray of an adjacent fiber. An interesting consequence is the generation of three cones, two of which are polarized, when a laser beam obliquely illuminates the fibers. These cones can be seen when viewing a light source through the mineral. Ulexite decomposes in hot water. See also *List of minerals *List of minerals named after people *Fiberscope a device that transmits images in much the same way *Calcite, another mineral with an optical property often illustrated in the same way. References External links *http://www.gc.maricopa.edu/earthsci/imagearchive/ulexite.htm *http://www.minerals.net/mineral/borates/ulexite/ulexite.htm Category:Sodium minerals Category:Calcium minerals Category:Borate minerals Category:Triclinic minerals * * * * * * * ca:Ulexita cs:Ulexit de:Ulexit el:Ουλεξίτης es:Ulexita fr:Uléxite gl:Ulexita it:Ulexite nl:Ulexiet ja:ウレキサイト pl:Uleksyt pt:Ulexita ru:Улексит fi:Uleksiitti sv:Ulexit